Binding of Candida albicans to immobilized amino acids and bovine serum albumin

In this study, we examined the binding of Candida albicans synchronized yeast-phase cells to plastic, immobilized amino acids and bovine serum albumin (BSA) and quantified the binding by using an XTT tetrazolium salt assay and absorbance determination. Our results show that C. albicans binds efficiently and specifically to several nonpolar aliphatic amino acids and positively charged amino acids and to BSA immobilized on tissue culture plastic but not to polar uncharged, negatively charged, or aromatic amino acids. Adhesion of yeasts to immobilized amino acids was not affected by preincubation of cells with BSA, whereas binding to immobilized BSA was affected by preincubation of yeasts with alanine, proline, and leucine but not by arginine or lysine. The ability to distinguish the chirality of these amino acids was also examined by using both the D and L amino acid configurations, and the results show that C. albicans yeasts recognize only the L configuration of these amino acids. The observations that C. albicans specifically binds to certain amino acids indicate that these amino acids may prove useful tools for studying the binding interactions of C. albicans yeasts with host proteins such as components of the extracellular matrix.

Stabilization of microtubule dynamics by estramustine by binding to a novel site in tubulin: a possible mechanistic basis for its antitumor action

The cellular targets for estramustine, an antitumor drug used in the treatment of hormone-refractory prostate cancer, are believed to be the spindle microtubules responsible for chromosome separation at mitosis. Estramustine only weakly inhibits polymerization of purified tubulin into microtubules by binding to tubulin (Kd, approximately 30 microM) at a site distinct from the colchicine or the vinblastine binding sites. However, by video microscopy, we find that estramustine strongly stabilizes growing and shortening dynamics at plus ends of bovine brain microtubules devoid of microtubule-associated proteins at concentrations substantially below those required to inhibit polymerization of the microtubules. Estramustine strongly reduced the rate and extent both of shortening and growing, increased the percentage of time the microtubules spent in an attenuated state, neither growing nor shortening detectably, and reduced the overall dynamicity of the microtubules. Significantly, the combined suppressive effects of vinblastine and estramustine on the rate and extent of shortening and dynamicity were additive. Thus, like the antimitotic mechanisms of action of the antitumor drugs vinblastine and taxol, the antimitotic mechanism of action of estramustine may be due to kinetic stabilization of spindle microtubule dynamics. The results may explain the mechanistic basis for the benefit derived from combined use of estramustine with vinblastine or taxol, two other drugs that target microtubules, in the treatment of hormone-refractory prostate cancer.

Nucleotide sequence of the gene coding for SEC14p in Candida (torulopsis) glabrata

A gene coding for SEC14p from Candida glabrata has been cloned and characterized. Nucleotide (nt) sequence analysis reveals an open reading frame of 909 bp and predicts the synthesis of a polypeptide of 302 amino acid (aa) residues. Comparison of nt and aa sequences shows that the gene exhibits a much higher homology to the Saccharomyces cerevisiae (72% and 87%, respectively) than to the Candida albicans (55% and 65%, respectively) SEC14 gene.

Carboxyl-terminal fragments of beta-amyloid precursor protein bind to microtubules and the associated protein tau

Alzheimer's disease is a neurodegenerative disorder characterized by protein depositions in intracellular and extracellular spaces in the brain. The intraneuronal deposits are formed by neurofibrillary tangles composed mainly of abnormally phosphorylated tau, a microtubule-associated protein, whereas the major constituent of the amyloid deposited extracellularly in the brain parenchyma and vessel walls is amyloid beta-protein (A beta). The proteolytic processing of the beta-amyloid precursor protein (beta PP) results in the generation of a complex set of carboxyl-terminal peptides that contain A beta. In this study, we have used fusion proteins containing carboxyl-terminal fragments of beta PP to investigate the association of beta PP with cellular components. We demonstrate that specific domains within the carboxyl end of beta PP contain binding sites for cytoskeletal components; one, within residues 1 to 28 of A beta, binds directly to tubulin, and the second one, within sequences carboxyl-terminal to A beta, binds tau and tubulin. We propose that the two neuropathological hallmarks of Alzheimer's disease, A beta deposition and neurofibrillary tangles, represent the residual of a disrupted beta PP-tubulin-tau complex.

Isolation and characterization of a gene encoding alpha-tubulin from Candida albicans

A gene encoding the alpha-tubulin of Candida albicans has been cloned and characterized. Nucleotide sequence analysis reveals the presence of an intron within the structural gene and predicts the synthesis of a polypeptide of 448 amino acid residues. Comparison of nucleotide and amino acid sequences with the Saccharomyces cerevisiae alpha-tubulin encoding genes shows a 75% homology and about 92% similarity respectively. In contrast to S. cerevisiae, C. albicans appears to possess only one gene for alpha-tubulin which is able to functionally complement a S. cerevisiae cold-sensitive tub1 mutant.

Estramustine phosphate but not estramustine inhibits the interaction of microtubule associated protein 2 (MAP2) with actin filaments

The effect of estramustine and estramustine phosphate (EP) on the interaction of microtubule associated protein 2 (MAP2) with actin has been examined. We show that (a) neither estramustine nor EP influences actin polymerisation (b) EP, but not estramustine, reduces the amount of MAP2 which co-sediments with F-actin in a dose-dependent manner and (c) EP decreases the MAP2-induced crosslinking of F-actin into gelled networks. The data suggest, that unlike estramustine, EP interacts with MAP2 and modifies its interaction not only with microtubules but also with actin filaments.

Antibiotics MDL 62,879 and kirromycin bind to distinct and independent sites of elongation factor Tu (EF-Tu)

Antibiotic MDL 62,879 inhibits bacterial protein synthesis by acting on elongation factor Tu (EF-Tu). In this study we show that the inhibition of protein synthesis by MDL 62,879 in an Escherichia coli cell-free system was fully reversed by addition of stoichiometric amounts of EF-Tu but not by large excesses of EF-Ts, ribosomes, or aa-tRNA. MDL 62,879 bound tightly to EF-Tu and formed a stable 1:1 MDL 62,879:EF-Tu (M:EF-Tu) complex. We show that binding of MDL 62,879 to EF-Tu strongly affects the interaction of EF-Tu with aa-tRNA and causes rapid dissociation of preformed EF-Tu.aa-tRNA complex, suggesting that inhibition of aa-tRNA binding is due to a conformational change in EF-Tu rather than competition for the aa-tRNA binding site. Indication of a conformational change in EF-Tu induced by MDL 62,879 is further confirmed by proteolytic cleavage experiments: MDL 62,879 binding strongly protects EF-Tu against trypsin cleavage. The observed effects of MDL 62,879 appear to be different from those of the kirromycin class of antibiotics, which also inhibit protein synthesis by binding to EF-Tu, suggesting two distinct binding sites. Indeed, the M:EF-Tu complex was able to bind stoichiometric amounts of kirromycin to form a 1:1:1 M:EF-Tu:kirromycin (M:EF-Tu:K) complex, providing direct evidence that the two antibiotics bind to independent and distinct sites on the EF-Tu molecule. The interaction of the M:EF-Tu:K complex with aa-tRNA and other co-factors suggest that the contemporary binding of the two antibiotics locks EF-Tu into an intermediate conformation in which neither antibiotic exhibits complete dominance.

The effects of antifungal agents on the morphogenetic transformation by Candida albicans in vitro

The effects of antifungal agents, with different mechanisms of action, on the morphogenetic transformation by synchronised yeast-phase Candida albicans cells in vitro and their respective anti-Candida activities are described. MIC data demonstrated that the azoles, amphotericin B and echinocandin were the most active agents against four C. albicans strains. Morphogenetic transformation experiments demonstrated that amphotericin B was significantly better at preventing the transformation, under a variety of test conditions, than the azoles and flucytosine: amphotericin B abolished the transformation at low concentrations while the azoles only prevented the morphogenetic transformation at much higher concentrations (> 100 x MIC).

Inhibitors of myo-inositol monophosphatase, ATCC 20928 factors A and C. Isolation, physico-chemical characterization and biological properties

During the course of a screening program for inhibitors of myo-inositol monophosphatase we fermented the strain ATCC 20928, a known producer of L-671,776. We now show that this strain produces a complex of at least three sesquiterpenic compounds, L-671,776 (termed factor B) and two structurally related substances, termed factors A and C. Both factors A and C, like L-671,776, exhibited inhibitory activity against myo-inositol monophosphatase. Six other fungi producing the above mentioned compounds were also isolated and taxonomically characterized.

Spectrophotometric determination of the morphogenetic transformation by synchronous Candida albicans: effects of antifungal agents

A spectrophotometric method for studying the morphogenetic transformation by Candida albicans is described. Synchronous yeast-phase C. albicans cells incubated at 35 degrees C formed germ-tubes and resulted in an absorbance increase at 340 nm but not at 595 nm. Furthermore, measurements of germ tube length increases correlated strongly (r2 > 0.95) with increases in absorbance at 340 nm during the morphogenetic transformation. Amphotericin B significantly affected the morphogenetic transformation, at the MIC and 1/10 MIC, whereby no increase in absorbance was observed at 340 nm. In contrast, identical measurements demonstrated that ketoconazole, at the MIC and 1/10 MIC, did not exhibit the same effects on the morphogenetic transformation by C. albicans cells.

Dephosphorylated but not phosphorylated microtubule associated protein MAP1B binds to microfilaments

We have reported that purified native MAP1B interacts with microtubules but not with microfilaments [Pedrotti and Islam, Cell Motil. Cytoskel. (1995) 30, 301-309]. However, MAP1B can be phosphorylated at multiple sites by casein kinase 11 (CKII) and proline-directed protein kinases (PDPK) and immunoblotting studies show that purified native MAP1B is phosphorylated at least at two CKII sites and at one PDPK site [Pedrotti et al., Biochemistry (1996) 35, 3016-3023]. We now show that phosphorylation affects the in vitro binding of MAP1B with microfilaments. Native MAP1B does not bind to microfilaments but after treatment with alkaline phosphatase the dephosphorylated MAP1B binds and cosediments with microfilaments. Dephosphorylation kinetics suggest that the PDPK site, but not CKII sites, may negatively regulate the interaction with F-actin. The ability of dephosphorylated MAP1B to crosslink microfilaments was also examined and showed that MAP1B exhibits only a weak crosslinking of F-actin when compared with MAP2.

Modulation of microtubule shape in vitro by high molecular weight microtubule associated proteins MAP1A, MAP1B, and MAP2

The effect of microtubule associated proteins on microtubule shape has been investigated in reconstitution experiments using purified tubulin and purified MAP1A, MAP1B, and MAP2. Microtubules assembled in the presence of these MAPs were fixed with 0.1% glutaraldehyde and, after negative staining, were examined by electron microscopy. The results show that MAP1A microtubules were generally short and "straight' while those assembled with MAP1B were longer and "bendy'. MAP2 microtubules showed both types of morphologies even though straight microtubules were more abundant. These data suggest that MAPs may modulate not only microtubule dynamics but also microtubule shape which may be important in their spatial distribution and/or role in specific neuronal areas.

Characterization of microtubule-associated protein MAP1B: phosphorylation state, light chains, and binding to microtubules

We have recently described a procedure for the purification of microtubule associated protein 1B (MAP1B) from calf brain [Pedrotti, B., & Islam K. (1995) Cell Motil. Cytoskeleton 30, 301-309], and this study further characterizes the purified protein and its interaction with microtubules. We show that purified MAP1B (1) is thermostable; (2) is mainly phosphorylated at the casein kinase II (CKII) sites but only partially phosphorylated at the proline-directed protein kinase (PDPK) sites; (3) both the CKII and PDPK sites can be dephosphorylated by alkaline phosphatase; and (4) dephosphorylation results in an increased mobility on SDS-PAGE gels. The ability of MAP1B to interact with microtubules was also examined and shows that (1) phosphorylated (1B-P), alkaline phosphatase-treated (1B-AP), and heat-treated (1B-P), alkaline phosphatase-treated (1B-AP), and heat-treated (1B-HT) MAP1B bind to taxol-stabilized microtubules; (2) 1 mol of 1B-P, 1B-AP, or 1B-HT each binds about 13-14 tubulin dimers; (3) light chain interaction with MAP1B heavy chain is not affected by AP- or heat-treatment; (4) MAP1B can be displaced from taxol-stabilized microtubules by titration with salt; (5) higher salt concentrations are required to displace 1B-AP compared with 1B-P from taxol-stabilized microtubules; and (6) MAP2 is able to displace both 1B-P and 1B-AP from taxol-stabilized microtubules. The role of phosphorylation in regulating MAP1B interaction with microtubules and light chains is discussed.

Transport of the antibacterial agent oxazolidin-2-one and derivatives across intestinal (Caco-2) and renal (MDCK) epithelial cell lines

The transepithelial passage of the orally bioavailable antibacterial agent oxazolidin-2-one (OXa) and 10 derivatives has been studied with human intestinal (Caco-2) and canine renal (MDCK) cell lines grown on polycarbonate filters. The transepithelial passage was assayed in the apical-to-basolateral (AP-to-BL) direction and in the opposite direction (BL to AP) in both cell lines. The observed passage rates of OXa were similar in both directions in the two cell lines, suggesting passive diffusion. This was further confirmed by the fact that transport kinetics were linear as a function of initial concentration. The rates of AP-to-BL passage of OXa and seven of the derivatives in both cell lines were linearly related to lipophilicity, whether expressed as high-passage liquid chromatography retention time or as the logarithm of the n-octanol-water partition coefficient (log P). These data suggest that the lipophilicity of OXa is important for its observed bioavailability after oral administration. Interestingly, three of the derivatives exhibited a higher passage rate than predicted by lipophilicity. Further studies indicated that this transport was saturable, similar in the two directions, and not affected by energy depletion, suggesting the presence of an additional carrier-mediated facilitated-transport mechanism.

beta PP and Tau interaction. A possible link between amyloid and neurofibrillary tangles in Alzheimer's disease

Extracellular deposition of amyloid fibrils and intraneuronal accumulation of paired helical filaments (PHFs) are the neuropathological hallmarks of Alzheimer's disease. The major constituent of amyloid fibrils is a 39- to 43-residue peptide (termed A beta), which is derived from a 695- to 770-amino-acid precursor protein (termed beta PP). The main component of PHFs identified so far is the microtubule-associated protein tau. Yet, there is no direct evidence of interconnection between these two pathological states. We report here that antibodies to an epitope located between residues 713 and 723 of beta PP770 (ie, the transmembrane region of beta PP distal to A beta) consistently labeled PHFs in the brain of Alzheimer patients. Solid phase immunoassay showed that a peptide homologous to residues 713 to 730 of beta PP770 bound tau proteins. This beta PP peptide spontaneously formed fibrils in vitro and, in the presence of tau, generated dense fibrillary assemblies containing both molecules. These data suggest that beta PP or beta PP fragments containing the tau binding site are involved in the pathogenesis of PHFs in Alzheimer's disease.

Microtubule associated protein 1B (MAP1B) promotes efficient tubulin polymerisation in vitro

The effect of MAP1B on tubulin polymerisation has been examined in reconstitution experiments using purified tubulin and MAP1B. Under the assembly conditions used, tubulin alone was incapable of polymerising, but addition of MAP1B resulted in rapid assembly into microtubules. The kinetics of MAP1B-promoted microtubule assembly examined using pseudo-first-order plots show that assembly is described by a single reaction rate. The calculated association rate constant for MAP1B was about 200 x 1096) M-1.s-1 and this constant was one order of magnitude higher when compared with that for MAP2-promoted assembly.

Effect of amino acid substitutions on calmodulin binding and cytolytic properties of the LLP-1 peptide segment of human immunodeficiency virus type 1 transmembrane protein

Previous studies have identified two highly basic amphipathic helical regions in the human immunodeficiency virus type 1 transmembrane protein that, in vitro, display both cytolytic and calmodulin-binding and -inhibitory properties that could contribute to cellular dysfunctions and cytopathogenesis during a persistent viral infection. In the current study, the structural specificity of the cytolytic and calmodulin-binding activities of the human immunodeficiency virus type 1 lentivirus lytic peptide (LLP-1) are examined with synthetic peptide homologs and analogs. The results of these studies demonstrate that even minor changes in LLP-1 amino acid content can markedly affect these properties, suggesting that sequence variation in these highly conserved LLP sequences may correlate with alterations in viral cytopathic properties.

Monochromosome transfers to Syrian hamster BHK cells via microcell fusion provide functional evidence for suppressor genes on human chromosome 9 both for anchorage independence and for tumorigenicity

We previously identified an anchorage independence-suppressor gene, SAII, on rat chromosome (RNO) 5. RNO5 is homologous to human chromosomes (HSA) 1 and 9. In order to find the human homolog of the SAII gene, we transferred HSA1 and HSA9 to an anchorage-independent and tumorigenic Syrian hamster BHK 191-5C cell line by microcell fusion. For HSA9, we used a t(X;9)-derivative chromosome to force the retention of this chromosome in hybrids by hypoxanthine-aminopterin-thymidine (HAT) selection. To study the possible effect of the X portion of the der(9)t(X;9), we also transferred a normal X to 191-5C cells. For HSA1, a neo-tagged chromosome was introduced. Following the transfer of der(9)t(X;9) to 191-5C cells, the hybrid cells became anchorage dependent and nontumorigenic, and, upon the loss of this chromosome, the cells regained their tumorigenic and anchorage-independent phenotypes. The transfer of HSAX or HSA1, on the other hand, affected neither of these phenotypes. These results provide functional proof of suppressor genes on HSA9 involving both anchorage independence and tumorigenicity. In addition, our data suggest the presence of another gene on HSA9 that causes a negative growth effect and whose phenotypic expression, contrary to the suppressor genes, is dosage dependent.

Comparison between thymidylate synthase B of Bacillus subtilis ATCC6633 and 168

Bacillus subtilis 168 possesses two thymidylate synthase genes: thyA and thyB, encoding for a thermolabile and a thermostable enzyme respectively. B. subtilis ATCC6633 also possesses two thy genes, both producing thermostable enzymes. A comparison of the thymidylate synthase B amino acid sequences from the two strains shows, among others, a Pro to Ala mutation which may affect the dUMP binding site. The apparent Km and Vmax values for dUMP and tetrahydrofolate were determined at a permissive temperature for both enzymes. The kinetic data showed a significant difference in the Km, but not in the Vmax, for dUMP between the two enzymes. The Km and Vmax for tetrahydrofolate were very similar.

Solubilization and identification of essential functional groups of Candida albicans oxidosqualene cyclase

The enzyme properties and location of essential functional groups of solubilized oxidosqualene cyclase of Candida albicans have been studied. We show that the C. albicans enzyme is much more heat-labile compared with Saccharomyces cerevisiae and rat liver cyclases, requires a histidyl residue for enzyme activity, contains an essential thiol residue either close to or in the active site and exhibits a carbocationic mechanism for catalysis, as the enzyme-bound substrate protects the enzyme from inactivation by a site-directed inactivator.